1. Field of the Invention
The present disclosure relates to low rotational torque radial ball bearings. The bearings of the present invention may be used, for example, in a general purpose motor and motors used in equipment such as data equipment and audio equipment. In particular, the present disclosure relates to retainer for a radial ball bearing having at least one channel to facilitate flow of lubricating oil.
2. Description of the Related Art
FIG. 10 shows a conventional radial ball bearing 100 having an outer ring 102 and an inner ring 104. Running channels (raceways) 106 and 108 are formed on outer ring 102 and inner ring 104 respectively. Running channel 106 is on the inner surface of outer ring 102. Running channel 108 is on the outer surface of inner ring 104. Running channels 106 and 108 are arc-shaped. A retainer 110 is located between inner ring 104 and outer ring 102. Balls 112 are supported in retainer 110 and are kept separate from each other with equal distance between any two adjacent balls 112. Retainer 110 rotates with the rotating ring of bearing 100. Balls 112 roll in running channels 106 and 108. The diameter of running channels 106 and 108 are greater than the diameter of balls 112. Thus, there is a radial gap between the surface of balls 112 and channels 106 and 108 except where balls 112 contact channels 106 and 108. A lubricant such as grease or lubricating oil is injected in bearing 100 to lower the sliding friction. The lubricant moves between running channels 106 and 108 due to the rotation of balls 112, thereby keeping the rolling surface of balls 112 lubricated.
In normal use, a preload in the axial direction is applied to radial ball bearing 100. The application of preload improves characteristics of radial ball bearing 100. For example, application of preload improves ball vibration control, rotational accuracy and rigidity. In FIG. 10 the axial preload is applied to inner ring 104 in X2 direction i.e. from the left side of radial ball bearing 100. When the preload is applied, the presence of the radial gap causes outer ring 102 and inner ring 104 to become offset in the axial direction relative to one another. The offsetting of inner ring 104 from outer ring 102 causes balls 112 to contact outer ring 102 and inner ring 104 at points A1 and B1 respectively. The line joining points A1 and B1, forms contact angle β with a vertical line passing through center of ball 112 as shown in FIG. 10, when inner ring 104 rotates clockwise when viewed from X1 direction, balls 112 along with retainer 110 orbit around inner ring 104 and in same direction as the direction of rotation of inner ring 104. At the same time balls 112 also turn around axis C1 D1 in the direction of arrow R1 as shown in FIG. 10. Line joining point A1 and point B1 is perpendicular to axis C1 D1 and they intersect at point O1 which is the center of ball 112.
When the rotational axis C1 D1 of balls 112 is tilted with respect to the bearing axial direction due to the application of preload, lubricating oil which moves between running channel 106 and running channel 108 is subjected to shear force when it passes between the inner wall of retainer 110 and balls 112. In this case, retainer 110 impedes smooth movement of lubricating oil and increases the mixing resistance of lubricating oil. This leads to increased bearing rotational torque, which in turn can cause heating or rotational unevenness, which in turn increases power consumption of device that uses radial ball bearing 100.
Therefore, it is desirable to provide a radial ball bearing wherein the shear force on the lubricating oil is reduced. It is further desirable to provide a retainer for radial ball bearing with contact surfaces that form a line contact with the balls of the radial ball bearing. It is also desirable that the boundary between the contact surface and the retainer surface is substantially parallel to a line drawn through the center of the balls, the line being perpendicular to the axis of rotation of the balls.